/* OICQ encryption algorithm
 * Convert from ASM code provided by PerlOICQ
 * 
 * puzzlebird@21cn.com, Nov-Dec 2002
 */


/********************************************************************
Notes: (OICQ uses 0x10 iterations, and modified something...)

IN : 64  bits of data in v[0] - v[1].
OUT: 64  bits of data in w[0] - w[1].
KEY: 128 bits of key  in k[0] - k[3].

delta is chosen to be the real part of 
the golden ratio: Sqrt(5/4) - 1/2 ~ 0.618034 multiplied by 2^32. 

0x61C88647 is what we can track on the ASM codes.!!
********************************************************************/
#include <arpa/inet.h>
#include <string.h>
#include "crypt.h"

void qq_encipher (
    unsigned long *const        v,
    const unsigned long *const  k,
    unsigned long *const        w)
{
  register unsigned long 
    y     = ntohl(v[0]),
    z     = ntohl(v[1]),
		a     = ntohl(k[0]),
    b     = ntohl(k[1]),
    c     = ntohl(k[2]),
    d     = ntohl(k[3]),
    n     = 0x10,
    sum   = 0,
    delta = 0x9E3779B9; /*  0x9E3779B9 - 0x100000000 = -0x61C88647 */

  while (n-- > 0) {
    sum += delta;
    y += ((z << 4) + a) ^ (z + sum) ^ ((z >> 5) + b);
    z += ((y << 4) + c) ^ (y + sum) ^ ((y >> 5) + d);
  }

  w[0] = htonl(y); w[1] = htonl(z);
}

void qq_decipher(
    unsigned long *const        v,
    const unsigned long *const  k,
    unsigned long *const        w)
{
  register unsigned long
    y     = ntohl(v[0]),
    z     = ntohl(v[1]),
    a     = ntohl(k[0]),
    b     = ntohl(k[1]),
    c     = ntohl(k[2]),
		d     = ntohl(k[3]),
    n     = 0x10,
    sum   = 0xE3779B90, // why this ? must be related with n value
		delta = 0x9E3779B9;

  /* sum = delta<<5, in general sum = delta * n */
  while (n-- > 0) {
    z -= ((y << 4) + c) ^ (y + sum) ^ ((y >> 5) + d);
    y -= ((z << 4) + a) ^ (z + sum) ^ ((z >> 5) + b);
    sum -= delta;
  }
   
  w[0] = htonl(y); w[1] = htonl(z);
}

/********************************************************************
 * encrypt part
 *******************************************************************/

void qq_encrypt (  
    unsigned char*  instr,
    int             instrlen,
    unsigned char*  key,
    unsigned char*  outstr,
    int*            outstrlen_prt)
{
  unsigned char 
    plain[8],         // plain text buffer
    plain_pre_8[8],   // plain text buffer, previous 8 bytes
    * crypted,        // crypted text
    * crypted_pre_8,  // crypted test, previous 8 bytes
    * inp;            // current position in instr
  int 
    pos_in_byte = 1,  // loop in the byte 
    is_header=1,      // header is one byte
    count=0,          // number of bytes being crypted
    padding = 0;      // number of padding stuff
  
  int rand(void) {    // it can be the real random seed function
    return 0xdead; }  // override with static number, convenient for debug
  
  /*** we encrypt every eight byte ***/
  void encrypt_every_8_byte (void) {
    for(pos_in_byte=0; pos_in_byte<8; pos_in_byte++) {
      if(is_header) { plain[pos_in_byte] ^= plain_pre_8[pos_in_byte]; }
      else { plain[pos_in_byte] ^= crypted_pre_8[pos_in_byte]; }
    } // prepare plain text
    qq_encipher( (unsigned long *) plain,
       		       (unsigned long *) key, 
         		     (unsigned long *) crypted);   // encrypt it
    
    for(pos_in_byte=0; pos_in_byte<8; pos_in_byte++) {
      crypted[pos_in_byte] ^= plain_pre_8[pos_in_byte]; 
    } 
    memcpy(plain_pre_8, plain, 8);     // prepare next
    
    crypted_pre_8   =   crypted;       // store position of previous 8 byte
    crypted         +=  8;             // prepare next output
    count           +=  8;             // outstrlen increase by 8
    pos_in_byte     =   0;             // back to start
    is_header       =   0;             // and exit header
  }// end of encrypt_every_8_byte
 
  pos_in_byte = (instrlen + 0x0a) % 8; // header padding decided by instrlen
  if (pos_in_byte) { 
    pos_in_byte = 8 - pos_in_byte; 
  }
  plain[0] = (rand() & 0xf8) | pos_in_byte;
  
  memset(plain+1, rand()&0xff, pos_in_byte++);
  memset(plain_pre_8, 0x00, sizeof(plain_pre_8));

  crypted = crypted_pre_8 = outstr;
  
  padding = 1; // pad some stuff in header
  while (padding <= 2) { // at most two byte 
    if(pos_in_byte < 8) { plain[pos_in_byte++] = rand() & 0xff; padding ++; } 
    if(pos_in_byte == 8){ encrypt_every_8_byte(); } 
  }
  
  inp = instr;
  while (instrlen > 0) {
    if (pos_in_byte < 8) { plain[pos_in_byte++] = *(inp++); instrlen --; }
    if (pos_in_byte == 8){ encrypt_every_8_byte(); }
  }

  padding = 1; // pad some stuff in tailer
  while (padding <= 7) { // at most sever byte
    if (pos_in_byte < 8) { plain[pos_in_byte++] = 0x00; padding ++; }
    if (pos_in_byte == 8){ encrypt_every_8_byte(); }
  } 
  
  *outstrlen_prt = count;
}


/******************************************************************** 
 * [decrypt part]
 * return 0 if failed, otherwise return 1
 ********************************************************************/

int qq_decrypt (
    unsigned char*  instr,
    int             instrlen,
    unsigned char*  key,
    unsigned char*  outstr,
    int*            outstrlen_ptr)
{
  unsigned char 
    decrypted[8], m[8],
    * crypt_buff, 
    * crypt_buff_pre_8, 
    * outp;
  int 
    count, 
    context_start, 
    pos_in_byte, 
    padding;

  int decrypt_every_8_byte (void) {
    for (pos_in_byte = 0; pos_in_byte < 8; pos_in_byte ++ ) {
        if (context_start + pos_in_byte >= instrlen) return 1;
        decrypted[pos_in_byte] ^= crypt_buff[pos_in_byte];
    }
    qq_decipher( (unsigned long *) decrypted, 
       	  	     (unsigned long *) key, 
        	  	   (unsigned long *) decrypted);
    
    context_start +=  8;
    crypt_buff    +=  8;
    pos_in_byte   =   0;
    return 1;
  }
  
  // at least 16 bytes and %8 == 0
  if ((instrlen % 8) || (instrlen < 16)) return 0; 
  // get information from header
  qq_decipher( (unsigned long *) instr, 
            (unsigned long *) key, 
            (unsigned long *) decrypted);
  pos_in_byte = decrypted[0] & 0x7;
  count = instrlen - pos_in_byte - 10; // this is the plaintext length
  // return if outstr buffer is not large enought or error plaintext length
  if (*outstrlen_ptr < count || count < 0) return 0;
  
  memset(m, 0, 8);
  crypt_buff_pre_8 = m;
  *outstrlen_ptr = count;   // everything is ok! set return string length

  crypt_buff = instr + 8;   // address of real data start 
  context_start = 8;        // context is at the second 8 byte
  pos_in_byte ++;           // start of paddng stuff
  
  padding = 1;              // at least one in header
  while (padding <= 2) {    // there are 2 byte padding stuff in header
    if (pos_in_byte < 8) {  // bypass the padding stuff, none sense data
      pos_in_byte ++; padding ++;
    }
    if (pos_in_byte == 8) {
      crypt_buff_pre_8 = instr;
      if (! decrypt_every_8_byte()) return 0; 
    }
  }

  outp = outstr;
  while(count !=0) {
    if (pos_in_byte < 8) {
      *outp = crypt_buff_pre_8[pos_in_byte] ^ decrypted[pos_in_byte];
      outp ++;
      count --;
      pos_in_byte ++;
    }
    if (pos_in_byte == 8) {
      crypt_buff_pre_8 = crypt_buff - 8;
      if (! decrypt_every_8_byte()) return 0;
    }
  }
  
  for (padding = 1; padding < 8; padding ++) {
    if (pos_in_byte < 8) {
      if (crypt_buff_pre_8[pos_in_byte] ^ decrypted[pos_in_byte]) return 0;
      pos_in_byte ++; 
    }
    if (pos_in_byte == 8 ) {
      crypt_buff_pre_8 = crypt_buff;
      if (! decrypt_every_8_byte()) return 0; 
    }
  }
  return 1;
}

/* This is the Public Function */
// return 1 is succeed, otherwise return 0
int qq_crypt (
    unsigned char   flag,
    unsigned char*  instr,
    int             instrlen,
    unsigned char*  key,
    unsigned char*  outstr,
    int*            outstrlen_ptr)
{
  if (flag == DECRYPT)
    return qq_decrypt(instr, instrlen, key, outstr, outstrlen_ptr);
  else if (flag == ENCRYPT)
    qq_encrypt(instr, instrlen, key, outstr, outstrlen_ptr);

  return 1; // flag must be DECRYPT or ENCRYPT
}
